Composite abrasive finishing tool

ABSTRACT

A GEAR-SHAPED ABRASIVE FINISHING TOOL AND THE METHOH OF FORMING SUCH A TOOL IN WHICH ATY LEAST A PORTION OF THE TOOTH ELEMENTS THEREOF ARE PROVIDED WITH WORKING FACES HAVING CONTROLLED VARIATIONS IN THEIR ABRASSIVE PROPERTIES SO AS TO PROVIDE A SELECTED ABRASIVE FISHING ACTION ON GEARS BEING FINISHED THEREBY.

Nov. 30, 1971 c. G. KOELLA 3,623,275

COMPOSITE ABRASIVE FINISHING TOOL Filed Nov. 10, 1969 s ink UnitedStates Patent O 3,623,275 COMPOSITE ABRASIVE FINISHING TOOL Charles G.Koella, Rochester, Mich., assignor to Michigan Tool Company Filed Nov.10, 1969, Ser. No. 875,383 Int. Cl. B24d 5/14 US. Cl. 51-206 R 8 ClaimsABSTRACT OF THE DISCLOSURE A gear-shaped abrasive finishing tool and themethod of forming such a tool in which at least a portion of the .toothelements thereof are provided with Working faces having controlledvariations in their abrasive properties so as to provide a selectedabrasive finishing action on gears being finished thereby.

BACKGROUND OF THE INVENTION Abrasive gear-shaped finishing tools of thegeneral type to which the present invention is applicable are in widespread commercial use for accurately finishing the surfaces of toothelements on workpieces such as gears, for example. conventionally, theabrasive finishing tool is mounted in a finishing machine such that thefinishing tool is disposed in tight meshing relationship with the gearto be finished. The disposition of the abrasive finishing tool relativeto the workpiece usually is at crossed axes and during the finishingoperation, the tool and workpiece are reciprocated longitudinallyrelative to each other during their rotation so that the full face widthof each tooth of the workpiece is traversed by the abrasive teeth of thegear-shaped finishing tool. Usually the direction of rotation of thefinishing tool and workpiece are reversed each time the direction oftraversing movement is reversed so that both faces of each gear toothare provided with an accurate surface finish and profile.

In accordance with the foregoing technique, corrections in dimensionalinaccuracies of hardened gear teeth, such as minor inaccuracies,involute profile, lead and runout caused during heat treatingoperations, can be readily accomplished. The correction of suchdimensional inaccuracies provides for improved contact patterns betweenthe working faces of mating gear teeth providing substantial reductionsin the operating noise level, as well as increased durability andoperating life of the gear train. This practice has now substantiallyeliminated the necessity of matching and lapping gears in pairs, whichconstitutes a costly and time-consuming practice.

While the foregoing technique has been found eminently satisfactory forabrasively finishing or honing the surfaces of most hardened gears, theuse of such abrasive gear-shaped finishing tools has not beensatisfactorily applied to finishing high-precision gears in whichdimensional tolerances must be maintained within millionths of an inch.In the finishing of such precision-type gears, it is frequently foundthat selective variations must be provided in the degree of finishingapplied to different portions of the working face of the gear teeth soas to provide finished gears which are Within the precise dimensionaltolerances. In accordance with the present invention, it is now possibleto selectively hone or abrasively finish gear teeth surfaces withoutdestroying areas which are within the precise dimensional tolerancesduring the finishing of other tooth areas that require stock removaland/ or surface polishing. Accordingly, extremely accurate honing ofprecision gears can now be achieved employing automatic finishingmachinery, thereby obviating the costly, time-consuming manual finishingmethods heretofore employed in correcting such precision gears.

SUMMARY OF THE INVENTION The foregoing and other advantages of thepresent invention are achieved by an abrasive gear-shaped finishing toolconsisting of a cylindrical body having a plurality of tooth elementsdisposed therearound which are adapted to be positioned in meshingrelationship with a workpiece to be finished. Each of the tooth elementsof the finishing tool includes a working face which is adapted to bedisposed in bearing contact with the corresponding face of gear teeth onthe workpiece. At least some of the tooth elements of the abrasivegear-shaped finishing tool are provided with working faces that are of acomposite construction consisting of a plurality of sections which areof controlled different abrasive finishing characteristics so as toprovide a corresponding controlled variation in the degree and type offinishing action imparted to the surfaces of the tooth elements ofworkpieces being finished.

In its method aspects, the present invention provides for a simple andeconomical process for forming abrasive finishing tools wherein at leastthe working faces of the tooth elements thereof can be provided withcontrolled variations in their abrasive properties consistent with theabrasive finishing action to be applied to precision gears. Inaccordance with this method, all or selected ones of the tooth elementscan be provided with variations in their abrasive properties along thelength of their working faces as well as selected variations in themagnitude of surface area of such variant abrasive characteristics.

Still additional advantages and benefits of the present invention willbecome apparent upon a reading of the description of the preferredembodiments taken in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary perspectiveview of a gearshaped finishing tool disposed in crossed axis meshingrelationship with a workpiece to be finished;

FIG. 2 is a fragmentary side elevational view, partly in section, of anabrasive gear-shaped finishing tool having a composite toothconstruction;

FIG. 3 is a transverse vertical sectional view taken through a typicalmold for casting the blank for preparing the composite gear-shapedfinishing tool; and

FIG. 4 is a fragmentary plan view of a portion of a mold of the typeshown in FIG. 3 having a gear-shaped blank positioned thereinpreparatory to a final casting operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to thedrawings, an abrasive gear-shaped finishing tool 6 is shown in FIGS. 1and 2 and comprises a cylindrical body having a plurality of toothelements 8 disposed therearound. The tooth elements 8 are conjugate toand are adapted to be disposed in tight meshing relationship with atoothed workpiece such as the gear 10 shown in FIG. 1. The finishingtool 6! is conventionally comprised of an inner hub section 12 which maybe of a synthetic, metallic or composite construction, around theperiphery of which the abrasive tooth elements are disposed. Thefinishing tool is adapted to be mounted on a spindle of a conventionalfinishing machine and is rotated in crossed axes relationship with thegear 10, while concurrently undergoing longitudinal reciprocation so asto provide the requisite abrasive finishing action on the working facesof the gear teeth.

The outer portion of the finishing tool 6, including the tooth elements8 thereon, is composed of an abrasive matrix comprising a mixture of asuitable binding agent in combination with a controlled proportion ofabrasive granules of a selected size and composition in furthercombination with various filler materials to impart the desired abrasivefinishing characteristics to the finishing tool. Conventionally, thebinding agent comprises a suitable synthetic resin, of which copolymersof polyainide resins and epoxy resins in accordance with the disclosureof US. Pat. 3,212,869 and polyurethane resins of the type disclosed inUS. Pat. 3,183,633, are conventionally preferred. The foregoing resinspossess the requisite strength and flexibility to provide satisfactoryfinishing operations of a large number of gear-shaped workpieces andpossess the requisite impact resistance, strength, wearresistance andresiliency to provide for a prolonged tool life. It will be understoodthat alternative satisfactory bonding agents including epoxy resins,phenolic resins, urea formaldehyde resins, synthetic rubbers, etc., canalso be satisfactorily employed in accordance with the practice of thepresent invention when they are compounded to provide the desiredphysical properties consistent with the intended end use of the abrasivefinishing tool.

Regardless of the specific chemical composition of the binding agentemployed, the abrasive matrix can contain abrasive particles incontrolled amounts up to about 80% of the total abrasive matrix. Theabrasive constituent itself can comprise any one of a variety offinely-particulated abrasive materials of the types well known in theart, including abrasive particles such as silicon carbide, aluminumoxide, diamonds, glass, silicon dioxide, etc. The size of the abrasiveparticles can broadly range from about 54 grit to about 500 grit and maycomprise particles which are all of substantially the same size or,alternatively, a mixture of particles of different sizes so as toprovide the desired abrasive finishing action. Abrasive particles havingparticle sizes of a magnitude of about 500 grit serve primarily as afiller to the resin binding constituent and impart an extremely finesurface finish to the work faces of tooth elements on a workpiece 'beingfinished thereby. On the other hand, abrasive particles of a larger gritsize usually in the range of 54 to 22 grit effect relatively rapid metalremoval from the tooth elements of the workpiece being finished.

The abrasive matrix can also include varying amounts of suitable fillermaterials which serve primarily as extenders of the resin abrasivemixture. Such fillers also contribute to the final physical propertiesof the abrasive tool, as well as imparting a desired surface finishingcharacteristic to the abrasive tooth elements. Conventionally,non-wicking or non-absorbent type filler materials are preferablyemployed which facilitate obtaining a homogeneous blend of the abrasivematrix and further add weight and strength thereto. Filler materials ofthe foregoing type which have been found satisfactory for this purposeinclude airborne silica, which is thixotropic and aids in maintaining asubstantially uniform suspension of the abrasive particles in thebinding agent during the setting or curing of the matrix after casting.Alternative filler materials which can be satisfactorily employedinclude fiber glass, calcium phosphate, calcium sulfate, zinc oxide,carbon black, graphite, etc.

In accordance with the foregoing, the abrasive matrix comprises thebinding agent, a controlled proportion of abrasive particles, and fillermaterials. Conventionally, the binding agent can be used in amountsranging from about 20% to about 80% by weight and preferably from about40% to about 60% by weight of the total abrasive matrix. The abrasiveparticles, on the other hand, are used in amounts up to about 80% byweight and, more usually, when abrasive action is desired, in amounts offrom about 30% to about 50%. Filler materials ordinarily are employed inamounts up to about 50% by weight, and more usually, in amounts of fromabout to about by weight. The specific amount of abrasive material usedwill depend on whether it is desired that selective portions of theworking face of the tooth elements of an abrasive finishing tool are toprovide an abrasive finishing operation or merely are intended toprovide a slight polishing operation without appreciably removing anymetal from the gear-shaped workpiece being finished.

A typical gear-shaped finishing tool in which the tooth elements are ofa composite construction is shown in FIG. 2. In the specific embodimentillustrated, the outer or addendum portion 14 of the tooth element iscomposed of an abrasive mixture which is integrally bonded andinterlocked to the dedendum portion 16, which is of a different abrasivematrix composition, providing thereby a working face 18 of each toothelement, which is of a composite construction and provides forcontrolled variations in its abrasive finishing characteristics. In thearrangement illustrated in FIG. 2, the addendum portion 14 extendsradially outwardly of the pitch circle 20, indicated in dashed lines,dividing the working face 18 of the abrasive tooth elements intosubstantially two equal sections. It is usually preferred, particularlywhen the addendum and dedendum portions of the tooth elements are ofsubstantially different abrasive cutting action, that the point ofjuncture between the addendum portion and dedendum portion be staggeredor offset between adjacent tooth elements so as to provide a blending ofthe abrasive finishing action on the tooth elements of a gear beingfinishing. This can satisfactorily be achieved in accordance with thepractice of the method aspects of the present invention by forming anoriginal abrasive finishing tool and thereafter machining or otherwiseremoving the tip portions of the abrasive tooth elements in a circularpattern disposed slightly eccentric or offcenter to the axis of thefinishing tool. In such manner, the radial depth of the addendum portion14 of the tooth element will vary around the entire finishing tool inaccordance with the dotted line indicated at 22 in FIG. 2, which isdisposed eccentric to the pitch circle 20 in an exaggerated relationshipfor the purposes of illustration.

It will also be appreciated that selected variations in the abrasivefinishing characteristics of such gear-shaped finishing tools can beachieved in which only certain ones of the tooth elements are providedwith a composite construction while remaining tooth elements consist ofthe same uniform abrasive matrix.

It will also be understood that the bonding agent used for differentsections of the composite tooth elements 8 of the finishing tool may beidentical to or may be of different chemical composition to provide thedesired re sultant physical and abrasive characteristics of thecomposite finishing tool. In accordance with the preferred bindingagents as disclosed in the two aforementioned US. patents, which areowned by the same assignee as the present invention, the abrasive matrixconsists of a polyamide cured epoxy resin or, alternatively, apolyurethane resin binder. The addendum portion preferably is comprisedof the epoxy polyamide resin binder which provides for a tenacious bondto the dedendum or hub portion of the finishing tool, which may be of asimilar resin binder or may also consist of a polyurethane-type bindingagent. In any event, the addendum portion is preferably mechanicallyinterlocked to the dedendum portion of the composite tooth element,further enhancing the strength of such a composite tooth structure andminimizing any tendency of separation of the two portions at theirparting lines. Typical of a variety of mechanical interlocking devicesthat can be satisfactorily employed for this purpose are aperturesindicated at 24 in FIGS. 2 and 4, which are provided and extend radiallyinwardly of the dedendum portions of the tooth elements which areadapted to become filled with and rigidly interlocked with the abrasivematrix of the addendum portion of the tooth element.

The specific abrasive characteristics of the addendum and dedendumportions 14, 16 of the tooth elements are selected so as to apply theappropriate corrective action to the faces of the gear-shaped workpiecesin accordance with the dimensional inaccuracies present. In thoseinstances where the gear workpiece is to receive finishing action alongthe dedendum portion of the tooth elements, the addendum portions of thebrasive finishing tool are provided with the desired type and quantityof abrasive particles, while the dedendum portion may be completelydevoid of any abrasive materials or may contain a lesser proportion ofsmaller grit size particles to impart only a minimal abrasive finishingaction to the addendum portions of the tooth elements on the workpiece.When the addendum of the tooth elements on a workpiece are to besubjected to abrasive corrective action, then converse formulation ofthe composite tooth elements of the finishing tool is provided to applythe desired localized and controlled corrective action withoutdisturbing those surfaces of the workpiece which are within permissibledimensional tolerances. It will be apparent from the foregoing thatlarge variations in the selected abrasive finishing characteristics ofcomposite finishing tools made in accordance with the practice of thepresent invention is feasible to adapt such finishing tools forautomatic finishing of precision gears, thereby eliminating theheretofore time-consuming manual correction of such dimensionalinaccuracies.

In accordance with the method aspects of the present invention, thecomposite gear-shaped finishing tool is prepared by employing a moldassembly as illustrated in FIGS. 3 and 4 of the drawing. The mold, asillustrated, consists of a circular base plate 26 on which an internalmaster gear 28 is detachably secured and is disposed with the toothelements thereof concentric to a central stud 30. In the specificembodiment shown, the hub 12 of the finishing tool is itself of acomposite construction and comprises an inner metallic hub section 32and a plastic rim section 34 securely bonded thereto and extendingradially outwardly therefrom to a point adjacent to the tooth elementson the master internal gear 28. The composite hub is clamped in positionon the base plate 26 by a clamping member 35, removably secured to thecentral stud 30. The space extending between the periphery of theplastic rim 34 and the internal gear mold 28 is adapted to be filledwith a suitable liquid mixture consisting of the resin bonding agent andappropriate proportions of suitable filler materials and/or abrasiveparticles consistent with the intended abrasive finishing action that isdesired with respect to the dedendum portion of the tooth elementsthereof. After a casting of the abrasive matrix and a curing thereof,the excess portion 36 overflowing the annular casting cavity is machinedaway and thereafter sections of all or selected ones of the resultanttooth elements are removed for a selected depth, enabling supplementalreplacement of the removed portions with an abrasive matrix of analternative abrasive finishing characteristic.

As previously indicated, it is preferred in accordance with the practiceof the present invention to remove the tip of the tooth elements of thepreliminarily formed abrasive finishing tool blank in a manner so thatthe points of the machined tooth elements lay in a circle which isdisposed eccentric to the pitch circle of the abrasive tooth elements.In this way, a controlled variation in the area of the two sections ofthe working faces of the tooth elements is achieved, providing a smoothtransition in the surface finish and contour of the tooth elements of aworkpiece finished thereby.

The resultant gear blank indicated at 38 in FIG. 4 is thereafterreinserted in a mold assembly of the same or similar type as that shownin FIG. 3, which similarly is provided with an encircling masterinternal gear 28. After placement of the finishing tool blank in themold assembly and a clamping thereof in appropriate registrationrelative to the master internal gear 28, the terminal cavities indicatedat 40 are filled with a liquid abrasive mixture which, upon subsequentcuring, becomes tenaciously bonded to the end portions of the toothelements of the 'blank. As previously indicated, it is usually preferredto provide a mechanical interlock between the dedendum and addendumportions of the composite tooth elements and this can be convenientlyachieved in accordance with the practice of the present invention bydrilling or otherwise machining suitable cavities, such as the apertures24, inwardly of the ends of the dedendum portions of the gear blank suchthat the second liquid abrasive mixture during casting thereof flowsinwardly of such apertures and upon curing becomes mechanicallyinterlocked therewith. Upon curing and/or hardening of the addendumsections of the composite finishing tool, it is removed from the moldassembly and finished, if necessary, along the side faces thereof toprovide the desired tooth width consistent with the intended end use ofthe finishing tool.

In order to further illustrate the practice of the present invention,typical examples are provided of suitable mixtures of binding agentscontaining abrasive particles which can be satisfactorily employed forforming composite tooth elements of the types previously disclosed. Itwill be understood that these examples are provided for illustrativepurposes and are not intended to be limiting of the invention as setforth in the subjoined claims.

EXAMPLE I A composite abrasive finishing tool is fabricated employing acomposite hub structure as shown in FIG. 3, which is placed in a moldassembly and a liquid resin abrasive mixture is poured in the annularcavity, effecting a filling thereof. The resin abrasive mixture has acomposition as follows:

Ingredient: Percent by weight Polyamide resin 40 Epoxy resin 20 Zincoxide filler 40 Total a 100 The polyamide resin used is commerciallyavailable from General Mills, Inc., under the designation ofVersamidel40, and is derived from the condensation of dibasicpolymerized fatty acids and polyamine having a resultant amine value of377, a specific gravity of 0.97 and a Brookfield viscosity of 5 poisesat C. The epoxy resin is commercially available from General Mills,Inc., under the designation Genepoxy-190, and is derived from thepolymerization of bis-phenol-A and epichlorohydrin, providing a resinhaving an epoxide equivalent value of 187-191, a Brookfield viscosity offrom about 11,000- 16,000 centipoises at 25 C., and a specific gravityof 1.18.

The mixture of the epoxy resin, polyamide resin and filler is made bygentle mixing to minimize entrapment of air and the resultant blend isthereafter allowed to stand for a period of twenty minutes to enableescape of the major portion of entrapped air bubbles. A suitable releaseagent, such as a silicon fluid designated as No. 20 available fromDow-Corning Corporation, is applied in the form of a solvent solution tothe surfaces of the mold, whereafter the volatile solvent consisting ofa mixture of toluene and alcohol is allowed to evaporate. The resultantresin mixture containing the filler is poured in the annular regionbetween the peripheral portion of the hub and the internal master gearand allowed to solidify at atmospheric pressure and at room temperaturefor a period of about 12 hours. Thereafter the excess portion of thecured mixture is trimmed from the upper surface of the blank afterextraction thereof from the mold and the tip portions of the toothelements are removed in a lathe employing a silicon carbide cutting toolwherein the tooth elements are eccentrically trimmed to .a point 20%outwardly of the pitch circle to a point 20% inwardly of the pitchcircle diametrically opposite thereto. The resultant machined gear blankis thereafter replaced in the mold assembly with a new coating ofrelease agent and a second resin abrasive mixture is prepared having acomposition as follows:

Ingredient: Percent by weight Polyamide resin 21.6 Epoxy resin 11.6Abrasive-8 grit silicon carbide 33.4 Abrasive-54 grit alumina 33.4

Total 100 The polyamide resin and epoxy resin are identical to thoseempolyed in preparing the blank of the abrasive finishing tool. Theresultant resin abrasive mixture similarly is mixed and is poured in theterminal tooth cavities 40 illustrated in FIG. 4 and is allowed to curefor a period of 12 hours at atmospheric pressure and at roomtemperature. The resultant composite tool is thereafter removed and theside surfaces thereof are trimmed, providing a finishing tool of thedesired width and possessing a dual abrasive finishing characteristicalong its working tooth surfaces.

EXAMPLE II A similar abrasive finishing tool having composite toothelements is prepared wherein a composite hub of the type employed inExample I is used in forming a blank with the peripheral portionconsisting of a resin abrasive mixture of the following composition:

Ingredient: Percent by weight Polyamide resin 19.9 Epoxy resin 13.3Abrasive-8O grit silicon carbide 33.4 Abrasive-54 grit alumina 33.4

Total 100 After casting and curing the gear blank, the tooth elementsthereof are machined as previously described in Example I and a 0-50resin filler composition consisting of 25% epoxy resin, 25% polyamideresin and 50% filler, consisting of carbon black and zinc oxide, isprepared which is cast in the peripheral cavities forming a compositefinishing tool. In this specific instance, the addendum portions of thetooth element of the finishing tool possess only minimal finishingaction, whereas the dedendum portions effect an abrasive finishingaction on the addendum portions of a workpiece to be finished.

EXAMPLE III A similar composite finishing tool is prepared in which apolyurethane resin is employed for forming the peripheral portion of thefinishing tool blank wherein the polyurethane resin comprises 30% byweight of the mixture with the balance consisting of a 50-50 mixture ofa No. 80 silicon carbide grit and-a No. 54 aluminum oxide grit. Theperipheral tooth tip portions of the finishing tool are composed of aresin abrasive mixture consisting of 21.9% polyamide resin, 11.6% epoxyresin, a 36-grit alumina abrasive present in an amount of 59.8% and thebalance a ZOO-grit alumina.

The foregoing composite finishing tool provides a higher abrasive actionalong the dedendum portions of the working faces of its tooth elementsand a lesser abrasive action along the addendum sections of the workingfaces thereof.

While it will be apparent that the description of the preferredembodiments are well calculated to provide the benefits and advantagesas herein described, it will be understood that the invention issusceptible to variation, modification and change without departing fromthe spirit thereof.

What is claimed is:

1. An abrasive gear-shaped finishing tool comprising a cylindrical bodyhaving a plurality of tooth elements therearound adapted to be disposedin meshing relationship with a workpiece to be finished, each of saidtooth elements including a Working face comprised of a bonded matrix, atleast a portion of said tooth elements being of a composite constructionwherein said working face thereof is divided into a plurality ofsections each having a different abrasive finishing characteristic inorder to impart selected variations in the abrasive finishing action ona workpiece being finished.

2. The abrasive gear-shaped finishing tool as defined in claim 1,wherein said working face of the composite said tooth elements isdivided into two radially displaced sections.

-3. The abrasive gear-shaped finishing tool as defined in claim 1,wherein all of said tooth elements of said finishing tool are of acomposite construction.

4-. The abrasive gear-shaped finishing tool as defined in claim 1,wherein at least the peripheral portion of said body and said toothelements are comprised of said bonded matrix.

5. The abrasive gear-shaped finishing tool as defined in claim 1,wherein the composite said tooth elements comprise a dedendum portioncomposed of a bonded abrasive matrix of a first composition and anaddendum portion of a bonded abrasive matrix of a second compositionprovided with a controlled different abrasive mixture, said addendum anddedendum portions tenaciously bonded to each other forming an integralcomposite tooth element.

6. The abrasive gear-shaped finishing tool as defined in claim 1,wherein at least one of said sections of said working face is composedof a bonded matrix substantially devoid of an abrasive particlestherein, thereby rendering that section substantially ineffectual inremoving material from a workpiece during a finishing operation.

7. The abrasive gear-shaped finishing tool as defined in claim 1,wherein said tooth elements terminate in a tip portion and said workingface of the composite said tooth elements is divided into two radiallydisplaced sections joined at a boundary disposed substantially parallelto said tip portion of said tooth elements.

8. The abrasive gear-shaped finishing tool as defined in claim 5,wherein said addendum portion and said dedendum portion include mutuallycoacting means for effecting a mechanical interlock therebetween.

References Cited UNITED STATES PATENTS 1,422,200 7/ 1922 Harris 51-20-72,815,746 12/ 1957 Schwarzkopf et a1. 51206 X 2,913,858 11/1959 Praeg etal. 51--206 R 2,980,966 4/1961 Praeg 51--2 06 R X 3,183,633 5/1965Decker 51206 R 3,550,330 12/1970 Nakamura 51-287 FOREIGN PATENTS 800,6808/1958 Great Britain 5l--206 R 864,688 4/ 1961 Great Britain 51206 RLESTER M. SWINGLE, Primary Examiner

